The present invention relates to a light source of new conception.
The object of the invention is to produce a planar, or substantially level, light source, flat or curved, which can be used for various types of lighting systems, in particular for lighting devices for motor vehicles, such as headlights and lamps, or for lighting devices inside buildings or outdoors, and lastly as reconfigurable light source for indicator and emergency panels.
With a view to attaining this object, the invention relates to a lighting device comprising a planar, or substantially level, flat or curved, rigid or flexible matrix of microfilaments integrated on a single substrate and suitable to emit light by incandescence when supplied by an electric current, said device comprising:
a reflecting or transparent substrate,
a plurality of metal microfilaments capable of emitting light by incandescence,
a grid of conducting tracks to supply the current to said microfilaments, applied to said substrate,
a transparent covering layer to permit emission of the luminous radiation, and
electronic control means to switch on part or all of the microfilaments of the matrix.
According to another characteristic, it is preferable to deposit a thin layer of nanoparticles on the reflecting substrate, with the function of converting, according to a multiphoton absorption process, part of the infrared radiation into visible light.
According to another characteristic, a vacuum is produced in the space inside the device, between the substrate and the covering layer. Alternatively, it is possible to fill this space with a mixture of inert gases to prevent oxidation of the microfilaments, or halogens, in order to increase the luminous efficiency. In this case an injection valve is provided to pump gas inside.
According to another characteristic, interposed between the substrate and the transparent covering layer are one or more intermediate layers, shaped in such as way as to improve control of the beam of light emitted.
It must be mentioned that the use of a matrix of microfilaments has already been proposed for the purpose of producing a display panel (see patent U.S. Pat. No. 5 956 003). Nonetheless, a matrix of microfilaments integrated in a structure of the type described above, for the purpose of producing a light source that can be used in lighting devices has not as yet been proposed.
The upper layer of the device according to the invention is produced with transparent material, such as glass or plastic material. It may be flat, have cavities to house the microfilaments, in order to enhance heat dissipation and limit divergence of the beam, or have a plurality of ridges for the purpose of directing the light beam. This layer must have a thickness capable of maintaining the vacuum or preventing escape of the gases used inside the source. The thickness must generally be greater than 0.5 mm and in the case that plastic material is used.
The substrate of the device according to the invention may be reflecting or transparent.
In the case of reflecting substrate, the radiation emitted by the filament is reflected by the substrate and is emitted from the device through the transparent covering layer. The reflecting substrate may have a flat surface or have cavities to reduce divergence of the beam emitted by the device. The reflecting substrate may be metal (such as in stamped metal plate) or composed of another material (such as glass, quartz, plastic, alumina or silicon) with a metal coating. In the case of metal plate a metal coating is also used to improve reflectance of the layer and reduce the temperature of the device. The metal coating (for example aluminium or silver) may be deposited by evaporation or sputtering. In both cases the reflecting substrate is an electric conductor and must therefore be insulated from the conducting tracks that supply current to the filaments. Insulation of the substrate is obtained with a coating of transparent dielectric material resistant to high temperatures (typically an oxide, such as silicon oxide or titanium oxide). The techniques used for deposition of this layer may be evaporation, dipping, sol-gel techniques or other known techniques.
In the case of transparent substrate (such as glass, quartz or plastic) the light emitted by the filament is emitted from the two opposed faces of the device, with the object of lighting on two sides (this may be useful in the case, for example, of an emergency light or signal). The transparent substrate may be flat, have cavities or a plurality of microridges on the surface with the object of reducing divergence and directing the light beam.
The cavities may be produced by stamping or using any other known technique. The surfaces of the substrate may be provided with housings for the conducting tracks. These housings may be produced simultaneously to the cavities and/or optics.
As already mentioned, at least one intermediate layer is preferably interposed between the substrate and the transparent covering layer. The purpose of the intermediate layer is to further limit divergence of the light beam emitted by the device. It may be produced with the same materials as the substrate and is typically composed of reflecting material. In this case it is also an electric conductor and must therefore be insulated from the supply tracks by an insulating layer. The intermediate layer has a plurality of holes, the internal surface of which has an additional optical function to the function of the cavities of the substrate. In fact, if we wish to house the microfilaments inside paraboloid microreflectors, the internal surface of the holes of the intermediate layer forms the upper section of the paraboloid, while the cavity of the substrate forms the lower part.
It is also possible to insert more than one intermediate layer, such as in the symmetrical configuration with transparent substrate, as shall be illustrated in detail hereunder.
The upper covering part, the intermediate layer and the substrate are provided with means suitable to maintain the vacuum or the internal gas atmosphere. This may be obtained using seals, by fusion or adhesion.
The metal filaments may be in tungsten or other tungsten-based metal alloys (such as rhenium-tungsten). The filaments may have a linear shape or be wound in a spiral to improve the overall luminous efficiency. Alternatively, it is possible to lay more than one filament, in the form of a winding, in line with the optical cavities, in order to improve the luminous efficiency, as will also be described in detail hereunder.
The tungsten microfilament may be laid continuously along all the metal tracks; nonetheless, it only reaches incandescence in the zones with the highest resistance between the ends of the rheophores, where the filament does not touch the track or is not parallel with the track.
The metal tracks in the substrate may be housed in specific seats made on the surface of the substrate and/or the intermediate layer.
The metal tracks may be produced by screen printing or ink-jet; alternatively it is possible to use metal plate tracks bonded to the substrate with appropriate resins. A further technique consists in starting from a single layer of sheet metal and producing the tracks using the etching technique (technology used for printed circuits). In this case the cavities in the substrate may be produced subsequently by removing the material from the substrate above the tracks.
To improve control of divergence of the beam it the conducting tracks may transgress inside the cavities. In this case the projecting ends may remain suspended in the cavities (if they have sufficient mechanical visibility) or may be supported by specific arms produced in the substrate simultaneously to the cavities.